The biosynthesis of histidine in Neurospora crassa

Abstract

The biosynthesis of histidine has been investigated using a series of histidine requiring mutants of Neurospora and Penicillium. A general method is given for the isolation of a number of imidazole derivatives that are accumulated by these mutants. Methods of degradation and chromatography have been used to identify with reasonable certainty three crystalline products as 4-(D-erythro-trihydroxypropyl)-imidazole, 4-(2-keto-3-hydroxypropyl)-imidazole and L-4-(2-amino-3-hydroxypropyl)-imidazole (L-histidinol). Evidence is presented to show that two other non-crystalline products are phosphate esters of the trihydroxy and the ketohydroxy compounds. Chromatographic evidence is presented which indicates two other compounds are imidazole acetic acid and 4-(2,3-dihydroxypropyl)-imidazole. A chemical synthesis of isomers of 4-(trihydroxypropyl)-imizadole is described. The trihydroxy, ketohydroxy, and aminohydroxy compounds have been placed in that order leading to histidine, on the basis of the sequence of the mutants and the accumulations by the double mutants. Evidence is discussed suggesting that the phosphate esters of these compounds are more likely to be the true precursors of histidine. A scheme is postulated for the relation of all these substances to histidine synthesis and the possibility that a pentose-5-phosphate may be an early precursor of histidine is discussed. A method for the paper chromatography of imidazoles is presented and the Rf values of numerous synthetic derivatives are given.